I have a set of 305 vortec heads they have 58cc chambers but they have a smaller intake valve than the L31s. Do you guys think if after some porting will they flow close to some untouched L31s? I want to port and polish them for my truck because I'm thinking that they will work way better than the stock swirl ports and I don't want to live heads just sitting there. Another question, What will my compression be on the original 350?

 

Welcome Aboard!

You should be able to safely enlarge the valve seats as long as you pay attention to valve rim shrouding. You may have to cut the chambers around the valves to accomodate them and allow perimeter flow. If the Vortec castings are prepared as the LT1 iron castings (as is reported) there should be more than adequate hardened depth of the exhaust seats to allow 1.60 valves.

Of course they'll flow better than swirlie heads. And the compression will depend largely upon the pistons installed. Are they flat or dished?

 

hate to burst your bubble,but vortec heads never came on a 305,nor did they come in 58cc chamber size.you have 305 centerbolt heads.vortec heads only have 8 intake bolts and have a taller than normal intake port.get a casting # from under the valve cover and post it here,and i'll tell you exactly what they are.
Eric B

 

Vortec heads did come on the 305s. Think 1996-2002 express with the 5.0 vortec. They are 58 cc chamber, 1.84" intake valves, 1.5" exhaust and flow like 229 cfm intake and roughly the same as the 350 vortecs on the exhaust.

 

But would the intake flow well with some porting? It doesn't bother me if it flows less as long there isn't much difference from an unported L31. What the compression be? I'm thinking about 9.8:1 it is the original L05 and yes the heads are vortec.

 

The 305 Vortec head are nothing close to the 350 vortec (906, 062) heads. The have smaller valves, a different runner shape, and a much different combustion chamber design. They don't really share much with the 350 vortec heads except the reaised runners. They are really just the old style 305 heads with raised runners.



The good news though, is that they can be made to flow close to vortec heads just like all other SBC heads with porting.

Essentially all the 305 Vortec heads are, are raised runner standard 305 heads.

 

Vortec heads were used on the L31 engine (350, 5.7 liter) and used on the L30 engine (305, 5.0 liter).

A flow bench comparison of the two appears here. Keep in mind that there were two similar L31 Vortec heads, one with a 062 casting number suffix and the other with a 906 suffix. I don't know if the L30 heads also had two versions.

In any event the web site shows the 305/5.0 L30 casting number 2332520 vs the 350/5.7 062 heads. For each lift and cfm block in the table, the 350 flow data appears above, and the 305 data appear below. It also appears that the 305 heads were altered to have 2.02/1.60 inch valves (based on what's in the table). The valve didn't seem to help much -- the 305 heads can't keep up with the intake of the 350, but are about the same as the exhaust on the 350. The 350 heads, meanwhile, flow very well and on-par with other flow data elsewhere on the web.

It's also not clear if the heads, either of the two listed, were ported in any way. So the data is helpful but not conclusive.

 

So its not worth it using them and having to buy the vortec intake?

 

Pretty much.

 

kdrolt, thanks for finding that and putting it up. Those were the "vortec" 305 I bought that had 2.02/1.60 valves installed and machined for .550 lift cam, but otherwise untouched as far as any gasket matching/port work. Same goes for the stock 062 castings, those were fresh outta the boneyard a freind had picked up and took to the same shop to have flowed and were in stock condition, no port work. Both flowed on the 600 Superflow at same shop so the info is as accurate as it's going to get.

As noted, the 305's are nowhere near the flow capability of the famious 350 vortecs due to runner and chamber design. Will they be as good as the LO3, I have'nt seen any flow sheet on those so I have no idea. Just from looking at flow numbers would not recommend the 305 "vortec" castings since they leave ALOT to be desired.

 

Thanks for the detail on those flow data.

Fast355 sent me the flow data on stock unported 187 casting number swirl port heads used on the E-code LO3 305 engine. The L30 Vortec 305 heads still flow better across the board, stock vs stock... which shouldn't be a surprise. At 0.500" lift the L30 heads went 199.4 cfm intake while the LO3 heads could only flow 165 cfm; at the same lift on the exhaust side the L30 heads went 177 cfm, while the LO3 heads went 140 cfm. Of course that's comparing a mid 90s head (with oversized valves added) to a mid 80s head (with stock valves).

A better comparison on other head flow data, 305 and 350, is summarized elsewhere on another thread by reading (or skipping) about 2/3rd into the thread.

Here's the 187 flow data from Fast335 PM'd to me::
---

(All flow data in cfm)

 

416 heads flow 195@ .500 bone stock,and you can pick up a fully rebuilt set with bigger valves for around $300. So yeah the 305 vortecs suck. Although I think pro topline makes a set with bigger valves and minor porting that outflow the 906 castings, but i dont know the price. Good Luck.

 

Thanks for all the info. So I guess Im going to have to start saving money for heads.

 

FWIW:

Member SSC posted a few months back about his Vortec 305-headed 305. He seemed pleased with the results.

Any chance not all Vortec 305 heads are created equal?

 

Oh, it is also possible to hurt flow with simple things like larger valves.

 

.... and they also flow 110 on the exhaust bone stock.

Question for discussion:

Is it better to have heads that flow 195/110 cfm i/e with minimal swirl like the 081/416 castings, or, is it better to have heads that flow 165/140 cfm i/e (187 castings) with a lot of swirl?

 

Depends upon what you want the motor to do, ie. peak power below 4000rpm or above.

 

As shown in this thread.

 

Can you mill the 350 Vortecs to fit the smaller bore 305? I read in an article somewhere, one of the chevy magazines that they did this, but they didnt say how or give details.

 

Yes you can and most people go this route. The average amount milled off is roughly .020.

 

The machine shop will know how to do it. If they don't, pick another machine shop quick!